Over-revving during gear change

Faults and Technical chat for the Hyundai Tucson
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BigMezza67
Posts: 7
Joined: Fri Mar 25, 2022 9:29 am

Post by BigMezza67 »

I have a Tucson Hybrid and, over the winter, I have noticed the gear change from 2 to 3 (I think) over-revs. The best way way to describe this is to imagine a manual gear change where your foot does not lift from the accelerator as the clutch is depressed and the next gear selection in made and the clutch then reengaged. (Hope that makes sense!)

It’s not due to hard acceleratIon, the revs increase from 2500 to 3000, before dropping back to 2000 after the gear change, but does only happen at lower temperatures (typically below 5degC) It only happens once. All other gear changes are normal.

Mentioned this to the Hyundai dealer when I took in it in for first service and they “need it overnight” to witness it.” That’s a fair comment, I guess. See you next December!!

Has anyone else had a similar problem?

jarvis
Posts: 84
Joined: Sun Mar 13, 2022 11:46 am

Post by jarvis »

See near the end of this article:
https://tech.hyundaimotorgroup.com/elec ... /hev-phev/

Amazingly the conventional auto box has no torque converter. Always uses electric motor to pull away and it helps with rev matching for gear changes.

Maybe in real cold weather, it can't use electric motor as a brake to slow the engine for up-shifts because the battery is too cold to take on the charge that would generate? Doesn't really explain the increase in revs though but if gear changes take longer in the cold, that might be the reason.
BigMezza67
Posts: 7
Joined: Fri Mar 25, 2022 9:29 am

Post by BigMezza67 »

Thanks for the reply. The local dealership certainly doesn’t have any idea!!
roadster
Posts: 206
Joined: Fri Feb 04, 2022 3:01 pm
Location: South Coast

Post by roadster »

jarvis wrote: Fri Mar 25, 2022 12:52 pm See near the end of this article:
https://tech.hyundaimotorgroup.com/elec ... /hev-phev/

Amazingly the conventional auto box has no torque converter. Always uses electric motor to pull away and it helps with rev matching for gear changes.

Maybe in real cold weather, it can't use electric motor as a brake to slow the engine for up-shifts because the battery is too cold to take on the charge that would generate? Doesn't really explain the increase in revs though but if gear changes take longer in the cold, that might be the reason.
Thanks for posting that link - very interesting! It would be even more interesting to see inside that Hybrid Control Unit. Is it a six speed epicyclic gearbox? Is it a dual clutch design with a combination of multi-plate clutches?

I very seldom actually notice a gear change and this is mostly when load requires a down change that the control system can't anticipate such as a steep incline. In the OP's case a sudden increase in engine RPM could just be part of the normal hybrid behaviour when the relatively small traction battery can't provide enough energy. My Toyota Hybrid would very noisily wake up the engine in a quite unpredictable way but of course my current PHEV has a much bigger battery capacity and is less likely to do this. I don't think there is a way of knowing which ratio is actually selected other than by observing the rev. counter or using the paddles to shift if your model has them.
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jarvis
Posts: 84
Joined: Sun Mar 13, 2022 11:46 am

Post by jarvis »

roadster wrote: Tue Mar 29, 2022 8:22 am Thanks for posting that link - very interesting! It would be even more interesting to see inside that Hybrid Control Unit. Is it a six speed epicyclic gearbox? Is it a dual clutch design with a combination of multi-plate clutches?

I very seldom actually notice a gear change and this is mostly when load requires a down change that the control system can't anticipate such as a steep incline. In the OP's case a sudden increase in engine RPM could just be part of the normal hybrid behaviour when the relatively small traction battery can't provide enough energy. My Toyota Hybrid would very noisily wake up the engine in a quite unpredictable way but of course my current PHEV has a much bigger battery capacity and is less likely to do this. I don't think there is a way of knowing which ratio is actually selected other than by observing the rev. counter or using the paddles to shift if your model has them.
Petrol and mild hybrid have 7-speed dual clutch where as hybrid and plug-in have 6 speed automatic. So planetary/epicyclic gear sets.

I think the hybrid control unit is the inverter, transformer and rectifier plus some ECUs. But the transmission is hiding underneath that as you look into the engine compartment.
Shahid0274
Posts: 2
Joined: Sun Sep 25, 2022 9:13 pm

Post by Shahid0274 »

Mine, 2020 HYUNDAI TUCSON SE NV48V MHEV CRDI started over revving in initial 3 gears after Auto start/stop malfunctioned. booked with dealer to be checked and one week later completely broke down on a motorway and never started again. Recovered to local Hyundai garage by AA and diagnosed that Auto start/stop pully on alternator jammed and caused the timing to go out and shattered the bits in engine.....and now waiting in garage for engine to be replaced, under warranty. SO DO NOT IGNORE IT!!!!!!!!!!!!!!!!!
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